Reflective coating, pigment, colored composition, and process of producing a reflective pigment

ABSTRACT

A reflective coating is disclosed that has a base layer provided with a reflective surface for reflecting electromagnetic radiation, such as visible and solar near-infrared light. The reflective coating also has a dielectric layer formed on the reflective surface, and an absorber layer. The absorber layer is formed on the dielectric layer that is formed on the base layer. The reflective coating has an average reflectance greater than about 60% for wavelengths of electromagnetic radiation in the range of 800 to 2500 nm that is irradiated upon the reflective coating. Additionally, the reflective coating has an average reflectance for wavelengths of electromagnetic radiation in the range of 400 to 700 nm irradiated upon the reflecting coating that is less than the average reflectance of the reflective coating from 800 to 2500 nm.

FIELD OF THE INVENTION

The present invention relates to reflective coatings, pigments, coloredcompositions, and processes of manufacturing reflective pigments forcool color products.

BACKGROUND OF THE INVENTION

Conventional reflective designs such as coatings, pigments and paintshaving varying optical properties of reflectance, transmittance, andabsorptance in different wavelength regions are known. Such designs areutilized in a variety of industries, and can be implemented on objectsto improve their optical properties. In particular, such designs providedifferent reflectance and absorptance values for electromagneticradiation (e.g., solar radiation) depending upon the wavelength of theelectromagnetic energy. Solar energy is mostly composed of visible lighthaving a wavelength in the 400 to 700 nm range (hereinafter visiblelight region) and solar near-infrared light having a wavelength in the800 to 2500 nm range (hereinafter solar near-infrared region).

In some designs, reflective pigments added to paint products can beutilized on the surface of objects such as buildings or other structuresto reduce how much solar energy is absorbed by the surface, converted toheat, and then transmitted into the buildings. This is because theoptical properties of the reflective pigments are formulated to increasereflectance values of visible light and/or solar-near-infrared light incomparison to stand alone non-reflective pigment added paint products.

Cool pigments are available commercially as ceramic or organic pigmentsand are typically used for cool paints that reflect, transmit, andabsorb visible and solar near-infrared light with values that differfrom conventional pigments. These cool paints absorb less solarnear-infrared light and reflect more solar near-infrared light thanpaints made with conventional colored pigments while providing a rangeof visual colors. However, because they also transmit solarnear-infrared light, cool paints are often painted on opaque white orother highly reflective backgrounds that increase the reflectance of thesolar near-infrared light; the white or highly reflective backgroundsreflect the light that is transmitted through the cool paint. However,it is not desirable for many applications to paint dark cool paints onbright, highly reflective backgrounds, because if the cool paint isscratched or disturbed, then the bright background color appears. Forexample, if a car, painted with a dark cool paint on a white background,was scratched so that the cool paint was removed and the backgroundcolor was exposed, then the scratch would appear white. This isundesirable since the dark car would then have a white scratch line.Therefore, it would be desirable to develop cool pigments that wereopaque, dark colored, had high solar near-infrared reflectance, and didnot require white or highly reflective backgrounds, so that they couldbe used in paints on dark color backgrounds, such as dark primercoatings.

Metallic flake pigments are also well known in the art and arecommercially available. However, there are no known designs for coolpigments that use metallic flake pigments that contain specificallydesigned multilayer coatings. Generally metallic flakes are designed forvisual colors only, or for visual colors that change with viewing angleto yield color shifting paints that are used for anti-counterfeitingapplications or for decorative paints. Since multilayer thin filmcoatings can be specifically designed by appropriate selection ofcoating materials and thicknesses to achieve properties that do notexist in ceramic or organic pigments, it would be advantageous ifmultilayer thin film coatings could be designed with optical propertiesappropriate for cool coatings and cool pigments that were superior toexisting cool pigments. It would be further advantageous if thesemultilayer thin film designs did not require bright or white reflectivebackgrounds for optimized reflectance.

In temperate climates that have buildings receiving considerable amountsof solar energy, it is desirable to reduce the amount of absorbed solarenergy that results in additional heating of buildings. This reductionin thermal heating of buildings enables lower energy costs duringcooling of such buildings, which is desired. Similar effects aredesirable in other objects, such as cars, etc. which are exposed tosolar heating and require cooling.

In many of the above described designs, however, there is a problem inthat color selection, especially for dark colors, is not availablewithout greatly reducing the solar near-infrared reflectance. Generally,conventional cool color coatings or paints have an average reflectancevalue in the solar near-infrared region of less than 50%. Ideally, sincesolar near-infrared energy is responsible for about half of the solarenergy that causes thermal heating in structures such as buildings,cars, and roofs, it is desirable to limit how much of this light isabsorbed by the structure. In particular, it would be desirable to havean average reflectance that is much greater than 50% in the solarnear-infrared light region.

The reflectance of visible light from an object determines the color ofthat object. Accordingly, it is also desirable to have an averagereflectance of a coating, pigment composition, etc. which coats anobject in the visible light range such that dark and bright colors canbe readily formed without loss of average reflectance in the solarnear-infrared region.

SUMMARY OF THE INVENTION

The problems of the conventional art are overcome with the presentreflective coating that increases an average reflectance ofelectromagnetic energy in the solar near-infrared region and has anaverage reflectance in the visible light region that ranges from brightto dark.

The invention disclosed herein describes new thin film designs forcoatings and pigments that have superior properties for cool coatingsand paints compared to existing multilayer thin film coatings known inthe art. In particular, designs are disclosed for opaque multilayer thinfilm coatings that have high solar-near-infrared reflectance for a widerange of colors, including dark colors which have low visualreflectance.

A reflective coating is disclosed that overcomes the problems ofconventional coating designs having an average reflectance less thanabout 50% in the solar near-infrared wavelength region and an averagereflectance in the visible wavelength region that is greater than thereflectance in the solar near-infrared region. The reflective coatingadvantageously can be optimized for different cool colors depending upona desired color. The reflective coating can also be designed to have awide range of designed colors with average visible reflectance valuesranging from less than 10% to greater than 60%, with solar near-infraredreflectance values that range from greater than about 60% to about 90%.The reflective coating is preferably opaque, so it does not require awhite or highly reflective background layer for improved solarnear-infrared reflectance.

In one embodiment of the invention, the reflective coating has a baselayer provided with a reflective surface for reflecting electromagneticradiation, and in particular visible and solar near-infrared light. Thereflective coating has a dielectric layer formed on the reflectivesurface, and an absorber layer formed on the dielectric layer. Forimproved spectral characteristics, the reflective coating is designed tohave an average reflectance greater than about 60% for wavelengths ofelectromagnetic radiation in the range of 800 to 2500 nm (solarnear-infrared region) that is irradiated upon the reflective coating.Additionally, the reflective coating design can have an averagereflectance for wavelengths of electromagnetic radiation in the range of400 to 700 nm (visible wavelength region) irradiated upon the reflectingcoating that is less than the average reflectance of the reflectivecoating in the solar near-infrared region. In another embodiment, theaverage reflectance is greater than about 75% for wavelengths ofelectromagnetic radiation in the range of 800 to 2500 nm.

In other embodiments, it is envisioned that additional dielectric andabsorber layers could be stacked upon the initial dielectric andabsorber layers with varying thicknesses to vary the characteristics ofthe reflective coating, such as average reflectance values and colors ofthe coating.

Another embodiment of the invention is a reflective pigment having abase layer provided with a top reflective surface and a bottomreflective surface. A dielectric layer is formed on the top and bottomsurfaces of the base layer, and an absorber layer is formed on thecorresponding layers of the dielectric layer formed on the base layer.The dielectric layer has an index of refraction at 550 nm in the rangeof about 1.3 to 2.5. Moreover, similar to the reflective coating, anaverage reflectance of the reflective pigment for wavelengths ofelectromagnetic radiation in the solar near-infrared range of 800 to2500 nm irradiated upon the reflective pigment is greater than about 60%and an average reflectance of the reflective pigment for wavelengths ofelectromagnetic radiation in the visible light range of 400 to 700 nmirradiated upon the reflecting coating is less than said averagereflectance of the reflective coating in the solar near-infrared range.It will be appreciated by those versed in the art that paints made usingthese reflective pigments will have solar near-infrared reflectancevalues lower than that of the reflective pigments, and that these paintreflectance values can be optimized by using well known techniques suchas adjusting the pigment volume concentrations, the percentage of otherconstituents, and by inducing leafing of the pigments. Furthermore, inother embodiments, the reflective pigment can have additional stackeddielectric and absorber layers depending upon desired averagereflectance values in the various wavelength regions and desired color.For most embodiments, the visual reflectance of reflective coatings from400 to 700 nm can range from near 0% to about 80%, but the solarnear-infrared reflectance from about 800 to 2500 nm is above 50%, andpreferably above 70%. The near-infrared solar radiation is greatest inthe range from about 800 nm to about 1500 nm, and is reduced in therange from 1500 nm to 2500 nm. It is desirable for the reduction ofsolar near-infrared heating that the reflectance of the coating orpigment to be highest in the range from 800 to 1500 nm, because thenear-infrared solar radiation is greatest in that range, so if thecoating reflectance is somewhat reduced in the range from 1500 to 2500nm, the effect is not substantial on the amount of near-infrared solarreflectance.

Unlike the reflective coating which provides a single reflectivesurface, the present reflective pigment provides two opposing surfacesthat act as reflective surfaces. Accordingly, the reflective pigment canbe added to paints and the like to improve their reflectivecharacteristics.

In yet another embodiment of the invention a colored composition isprovided and includes a polymer medium and a plurality of reflectivepigments. The reflective pigments are dispersed in the polymer medium,and are formed in a manner similar to the reflective pigment discussedabove. The polymer medium can be, for example, a paint or ink that hasimproved spectral characteristics due to the addition of the pigments.

A process of producing a reflecting pigment is also disclosed and hassteps of providing a releasable substrate with a first absorber layerthereon. Next, a first dielectric layer, a metallic base layer, a seconddielectric layer, and a second absorber layer are stacked in this orderon the first absorber layer. In additional embodiments, a polymer layercan be stacked on the second absorber layer, and/or it can be used asthe initial stacking layer on the releasable substrate, or it can be inthe above structure where the metallic base layer is replaced by ametallic base layer/polymer layer/metallic base layer structure. Theprocess also includes a step of removing the releasable substrate fromthe first absorber layer or polymer layered structure to produce areflecting pigment.

These and other advantages of the invention will become apparent topersons of reasonable skill in the art from the following detaileddescription, as considered in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-section of a first embodiment of a reflective coating;

FIG. 2 is a cross-section of a second embodiment of a reflectivecoating;

FIG. 3 is a cross-section of a third embodiment of a reflective coating;

FIG. 4 is a cross-section of a fourth embodiment of a reflectivecoating;

FIG. 5A is a cross-section of a first embodiment of a reflective pigmentformed on a release coated Mylar substrate;

FIG. 5B is a cross-section of the first embodiment of the reflectivepigment of FIG. 5 a;

FIG. 6 is a cross-section of a second embodiment of a reflectivepigment;

FIG. 7 is a cross-section of a third embodiment of a reflective pigment;

FIG. 8A is a cross-section of a fourth embodiment of a reflectivepigment;

FIG. 8B is a cross-section of a fifth embodiment of a reflectivepigment;

FIG. 9 is a cross-section of a sixth embodiment of a reflective pigment;

FIG. 10 is an exemplary reflectance versus wavelength plot showingcharacteristics of a cool color reflective coating;

FIG. 11 is another reflectance versus wavelength plot showing exemplarycharacteristics of another cool color reflective coating; and

FIG. 12 is a flow chart illustrating a process of producing a reflectivepigment and colored composition.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following is a detailed description of certain embodiments of theinvention presently contemplated by the inventor to be the best mode ofcarrying out his invention.

Generally, embodiments of the present invention are directed to areflective coating, reflecting pigment, color composition, and processfor forming a reflective pigment that have improved spectralcharacteristics over conventional coatings and pigments used in coolcolor paints and other cool color products. Embodiments of the presentinvention use alternating layers of dielectric and specific absorberlayers formed on a base layer that are fine tuned to provide an array ofcool colors depending upon the thicknesses and number of layers providedon the base layer. The absorber layers have specific properties in thatthe light absorption of the absorber material decreases as thewavelength increases from 400 to 700 nm, which is the visible wavelengthrange, and the absorber layers are substantially non-absorbing in thesolar near-infrared region of 800 to 2500 nm.

These characteristics of the above dielectric and absorber layersfacilitate manufacture of coatings, etc. having specific spectralproperties that are advantageous over conventional coatings. Forexample, embodiments of the invention have an average reflectance forelectromagnetic radiation in the range of 800 to 2500 nm irradiated ontothe coating that is greater than 60%. Moreover, these embodiments alsohave spectral characteristics for electromagnetic radiation in the 400to 700 nm region irradiated upon the coating that can be less than theaverage reflectance in the 800 to 2500 nm range. In another embodiment,the average reflectance is greater than about 75% for wavelengths ofelectromagnetic radiation in the range of 800 to 2500 nm.

Turning now to FIG. 1, an embodiment of a reflective coating, showngenerally as 10, includes a base layer 12. Materials of the base layer12 are selected so as to have the reflective characteristics suitablefor the intended use of the reflective coating 10. The presentlypreferred base layer 12 is a metal layer, and in particular an opaquealuminum (Al) layer. Aluminum is a generally inexpensive material thathas good reflectance characteristics in both the visible andnear-infrared wavelength range. Additionally, aluminum can be readilyformed into thin layers by conventional processes such as sputtering orevaporation. It will be appreciated in view of the teachings herein,however, that other metal layers can be used in place of aluminum.

By way of example, the base layer 12 can be formed from aluminum,copper, silver, gold, platinum, palladium, nickel, copper, cobalt,niobium, chromium, titanium, tin, and combinations or alloys of these orother reflective metals. Other reflective materials include, but are notlimited to lanthanide and transition metals including combinationsthereof. The thickness of the base layer 12 can be in the range fromabout 100 nm to about 200 nm, although this range should not beconstrued as restrictive. Different reflector materials may requireother thicknesses of the base layer to obtain desired spectralcharacteristics, namely a reflective coating that has near maximumreflectance for that material from 400 to 2500 nm and is visuallyopaque. For example, in one embodiment discussed herein an aluminum baselayer has a preferred thickness of 200 nm. However, an aluminum layerhaving a thickness of about 30 to 250 nm or even thicker can be used, aslong as the aluminum is opaque and has high reflectivity of greater thanabout 90% at wavelengths from 400 to 2500 nm.

As further shown in FIG. 1, the base layer 12 has a dielectric layer 14formed thereon. Different processes can be used to form the dielectriclayer 14 on the base layer. These processes include physical vapordeposition, such as sputtering, thermal evaporation, or electron beamevaporation, chemical vapor deposition, or other thin film depositionprocesses well known to those versed in the art. The preferable methodsare the physical deposition methods of reactive sputtering or reactiveevaporation, with the preferred method being reactive magnetronsputtering from dual sputtering targets using mid-frequency acsputtering. Generally, the dielectric layer 14 preferably has an indexof refraction at 550 nm of about 1.3 to 2.5 and an extinctioncoefficient for electromagnetic radiation in the wavelength range of 400to 2500 nm of less than about 0.1. More preferably, the index ofrefraction at 550 nm is between 1.4 and 2.2 and the extinctioncoefficient from 400 to 2500 nm is less than about 0.01, most preferablyessentially zero.

The dielectric layer 14 can be inorganic, since these materials havegood rigidity and brittleness properties for conversion of the coatinginto a pigment. In one preferred embodiment, the dielectric layer 14 isa silicon nitride (SN) layer. However, other dielectric materials thatcan form the dielectric layer include, but are not limited to, metalfluorides, metal oxides, metal sulfides, metal selenides, metalnitrides, metal carbides, and combinations thereof. Generally, it isenvisioned that transparent and substantially non-absorbing materials inthe 400 to 2500 nm wavelength range may be used as a dielectric layer.

The thickness of the dielectric layer 14 generally varies in the rangefrom about 10 nm to about 220 nm, although this range should not beconstrued as restrictive. Different dielectric materials may requireother thicknesses of the dielectric layer 14 to obtain specificreflective properties of the reflective coating. In one embodimentdiscussed herein, a silicon nitride layer has a preferred thickness of104 nm.

An absorber layer 16 is formed on the dielectric layer. Similarprocesses as described with respect to the dielectric layer 14 can beused to form the absorber layer 16, although sputtering is currentlypreferred. The absorber layer 16 may be formed of a semiconductormaterial. In particular, the structure of the semiconductor can beamorphous. The preferred embodiment of this design uses the absorberlayer to absorb light in the visible region from 400 to 700 nm, whichallows designs with a wide range of colors to be obtained, includingdark colors. As is well known to those versed in the art of thin filmdesign, highly reflective coatings in given wavelength regions are bestobtained when the thin film layers are not absorbing in that wavelengthregion. Since cool coatings are most efficient if they have highreflectance in the non-visible part of the solar spectrum, which is thenear-infrared solar wavelengths from about 800 to 2500 nm, it istherefore desirable that the absorber layer that is absorbing from 400to 700 nm not be substantially absorbing from 800 to 2500 nm.Semiconductor materials are preferred materials for this application,since they are absorbing at wavelengths less than the band gapwavelength and are non-absorbing at wavelengths greater than the bandgap wavelength. Therefore, a preferred material for use as an absorberlayer would be one with a band gap wavelength corresponding to about 700to 800 nm. This band gap wavelength corresponds to a band gap energy of1.55 to 1.77 eV. This band gap energy range encompasses that ofamorphous silicon.

An amorphous silicon (Si) layer having a band gap of about 1.7 eV mayform the absorber layer 16. For such an amorphous silicon layer, it ispreferred to sputter deposit the layer in a vacuum web coater. However,other materials having a similar band gap are envisioned as capable ofbeing used as an absorber layer. Generally, the absorber layer 16described herein has specific properties that differ from conventionalabsorber layers. First, the present absorber layer 16 is substantiallynon-absorbing in the solar near-infrared region. Conventional absorberlayers, which are often metals, generally remain absorbing in thisentire wavelength region. The preferred extinction coefficient of theabsorber layer 16 is less than about 0.3 at 800 nm and is less thanabout 0.1 at wavelengths greater than about 1000 nm.

Importantly, the silicon absorber layer is preferably sputtered fromsilicon sputtering targets using methods well known to those versed inthe art. The silicon sputtering targets that are commonly used havetypical compositions ranging from 100 weight % silicon-0 weight %aluminum to about 90 weight % silicon-10 weight % aluminum, with apreferred composition of 98 weight % silicon-2 weight % aluminum to 94weight % silicon-6 weight % aluminum. Therefore, the preferred amorphoussilicon material used as an absorber layer in these preferredembodiments contains about 2 to 6 weight % aluminum. The preferredsilicon nitride dielectric layer is also preferably reactively sputteredusing these preferred silicon sputtering targets.

Additionally, the refractive index n and extinction coefficient k ofabsorber layer 16 varies with wavelength in the visible light region.For example, for absorber layer 16, n can be about 4.5 and k can beabout 2.0 at 400 nm and n can be about 4.3 and k can be about 0.4 at 700nm, and n can be about 4.0 and k can be about 0.1 at 1000 nm.Conventional absorber layers generally do not have this type ofcharacteristic in the visible light region in combination with the nearnon-absorbing property in the solar near-infrared region.

The thickness of the absorber layer 16 generally varies in the rangefrom about 10 nm to about 100 nm, although this range should not beconstrued as restrictive. Different absorber materials may require otherthicknesses of the absorber layer to obtain specific spectral propertiesof the reflective coating. In one embodiment discussed herein, anabsorber layer is formed as a silicon layer having a thickness of about56 nm on an aluminum base layer 12 having a reflective surface 18.

FIG. 2 illustrates a second embodiment of a reflective coating 20. Inthis and the following embodiments of the reflective coatings, likelayers of the previous embodiments of the reflective layer are similarlydesignated for simplicity. Moreover, it is envisioned that differentcharacteristics of the various embodiments of the reflective coatingsdiscussed herein can be interchanged with other embodiments as is knownto those skilled in the art.

As shown in FIG. 2, the base layer 12 has the first dielectric layer 14and absorber layer 16 formed thereon. Additionally, a second dielectriclayer 22 is formed on the absorber layer 16. This structure enables acool color reflective coating to be formed, which has different colorand reflectance from that described in FIG. 1.

The second dielectric layer 22 is similar to the first dielectric layer14, however the thicknesses of the layers can vary, with the thicknessof the second dielectric layer 22 generally being different than thefirst dielectric layer 14. For a first dielectric layer 14 having athickness in the range of 10 to 220 nm, the absorber layer 16 having athickness of about 10 to 100 nm, it is envisioned that the seconddielectric layer 22 can have a thickness of about 25 to 250 nm.Additionally, the second dielectric layer 22 can have an index ofrefraction at 550 nm of about 1.3 to 2.5 and an extinction coefficientfor electromagnetic radiation in the wavelength range of 400 to 2500 nmof less than about 0.1.

Turning now to FIG. 3, a third embodiment of a reflective coating isgenerally designated as 30. In this embodiment, a second absorber layer32 is formed on the second dielectric layer 22. For a first dielectriclayer 14 having a thickness in the range of 10 to 220 nm, a firstabsorber layer 16 having a thickness of about 10 to 100 nm, a seconddielectric layer 22 can having a thickness of about 90 to 200 nm, it isenvisioned that the second absorber layer 32 can have a thickness in therange of about 1 to 200 nm.

FIG. 4 illustrates a fourth embodiment of a reflective coating, which isgenerally designated as 40. Unlike the other reflective coatings, thisreflective coating has a third dielectric layer 42 formed on the secondabsorber layer 32. The third dielectric layer 42, similar to the otherdielectric layers, can have an index of refraction at 550 nm of about1.3 to 2.5 and an extinction coefficient from 400 to 2500 nm of lessthan about 0.1. Moreover, the third dielectric layer 42 like the otherdielectric layers 14, 22 can be formed of silicon nitride.

This structure of the reflective coating 40 enables different colors andreflectance values to be formed compared to the other embodiments 10,20, and 30 of the reflective coating. The thicknesses of the dielectriclayers can vary like the other embodiments. In one preferred embodiment,the first dielectric layer 14 formed on the reflective surface 18 of thebase layer 12 can have a thickness of about 30 to 150 nm, and theabsorber layer 16 formed on the first dielectric layer can have athickness of about 40 to 80 nm. Furthermore, the second dielectric layer22 can have a thickness of about 90 to 200 nm, the second absorber layer32 can have a thickness of about 2 to 10 nm, and the third dielectriclayer can have a thickness of about 30 to 500 nm. In general,embodiments with additional layers provide additional design flexibilityto achieve a wider range of colors and high near-infrared reflectancevalues.

Similar to the other embodiments, the base layer 12 can be a metallayer, such as an aluminum layer. The absorber layers 16, 32 can be asemiconductor, such as amorphous silicon. Moreover, the absorber layerscan have an n/k value greater than about 10 at 700 nm and greater thanabout 100 at 1250 nm, where n corresponds to the refractive index of theabsorber layers and k is the extinction coefficient of the absorberlayers. In other embodiments, the absorber layers can be formed ofamorphous silicon with the dielectric layers formed of one or more ofsilicon nitride, silicon dioxide, nitrides, oxides, fluorides or othercomparable low refractive index materials that are substantiallytransparent from 400 to 2500 nm.

A first embodiment 50 of a reflective pigment 52 formed on a releasablesubstrate 54 is shown generally in FIG. 5A. As is known to those skilledin the art of pigment design, the reflective pigment 52 can be utilizedin various mixtures to add color to a base composition such as a polymerto form a color composition. Such compositions can include mixtures suchas paints or inks, which provide improved spectral properties to thesurfaces coated by the paints or inks. Since the reflective pigment 52is dispersed within the paint or ink, there are improved reflectanceproperties of the paint/ink. For example, reflective pigments used withthe present invention advantageously provide a paint/ink having improvedspectral properties such that for wavelengths of electromagneticradiation in the solar near-infrared range, an average reflectance ofsuch electromagnetic radiation is greater than about 50%. Moreover, inthe visible light range of 400 to 700 nm, the reflectance is less thanthe average reflectance in the solar near-infrared range of 800 to 2500nm.

Unlike the reflective coatings 10, 20, 30, and 40 that generally haveone reflective side surface that is coated, the reflective pigment 52has a central layer formed as a base layer 56. Preferably, the baselayer 56 is formed of a metal layer, such as opaque aluminum with bottomand top reflective surfaces 58, 60 respectively that facilitatereflection of electromagnetic radiation.

The reflective pigment 52 is formed on the releasable substrate 54,which can be a thin film. In FIG. 5A, the releasable substrate 54 is aMylar film 62 having a soluble release layer 64 coated thereon. Stackedlayers are then formed on the release layer 64 so that a dielectriclayer 66 is formed on the top and bottom surfaces 58, 60 of the baselayer 56. As used herein with respect to the embodiments of a reflectivepigment, a layer refers to coatings symmetrically arranged above andbelow the base layer.

An absorber layer 68 is formed on the dielectric layer 66, which isformed on the base layer 56. As shown in FIG. 5A, it is necessary todeposit the absorber layer and dielectric layer twice to provide thearranged stacked structure of the reflective pigment 52 having adielectric layer 66 and absorber layer 68.

Upon completion of the stacked structure, the reflective pigment 52 isremoved from the releasable substrate 54. FIG. 5B shows a stand-alonereflective pigment 52. Similar to the reflective coating dielectriclayers, the dielectric layer 66 of the reflective pigment 52 can have anindex of refraction at 550 nm of about 1.3 to 2.5. The thicknesses ofthe dielectric layer 66 can be about 10 to 220 nm, and the thickness ofthe absorber layer 68 can be about 10 to 100 nm. Additionally, thereflective pigment 52 has an average reflectance for wavelengths ofelectromagnetic radiation in the solar near-infrared region irradiatedupon the reflective pigment that is greater than about 60%, and anaverage reflectance for visible light irradiated upon the reflectingcoating which is less than the average reflectance in the solarnear-infrared region. The reflective pigment 52 can be added todifferent mixtures to improve spectral properties of the mixtures. Itwill be apparent to those versed in the art that the properties of anindividual pigment 52 will be the same as those for the coating 50 ifthe pigment dimensions are about a factor of 10 greater than the largestwavelength to be reflected. Since the reflectance of these designs arehigh up to 2500 nm or 2.5 microns, the pigment reflectance should benearly the same as the coating reflectance for pigment sizes greaterthan about 25 microns. Here size means the typical width and length ofthe pigment, not the thickness of the pigment. The properties of thepaint that is made from these pigments will differ from the pigmentproperties, depending on the pigment volume concentration and otherpaint formulation constituents. In one embodiment, the reflectivepigment 52 is dispersed in a polymer medium that is substantiallytransparent from 400 to 2500 nm, for example with transmittance ofgreater than 90%, to provide a colored composition. This coloredcomposition can be used as an ink or paint, for example, and hasimproved reflectance properties relative to conventional paintcompositions. The polymer medium into which the reflective pigment isdispersed preferably has a long-wave infrared absorption from 5000 nm toabout 40,000 nm that exceeds 60%. High long-wave infra-red absorptionresults in high long-wave infra-red emittance, which also results in thecolored composition remaining cooler. Moreover, since the thicknesses ofthe various dielectric and absorber layers can be selected, differentcolors can be made. Furthermore, for structures such as buildings usingthe colored compositions, lower heating of the buildings can be realizeddue to the improved reflectance of electromagnetic energy in the solarnear-infrared wavelength range and high long-wave infrared emittance.

FIG. 6 shows another embodiment of a reflective pigment 70. Although notshown, the reflective pigment 70 is formed on a releasable substratesimilar to that shown in FIG. 5A. The reflective pigment is similar tothe reflective pigment 52 shown in FIG. 5B, and has similar layersidentified with the same reference numbers. However, an outer polymerlayer 72 is formed on the absorber layer 68. The polymer layer 72 canhave a thickness of about 1000 to 3000 nm. Preferably, the polymer layeris formed of an acrylic, but can be formed of any suitable polymer thatis substantially transparent for electromagnetic radiation withwavelengths from 400 to 2500 nm. The polymer layer can be used to reducethe density of the reflective pigment and also increase the volume ofthe pigment in a cost-effective manner, since polymer layers are low incost and can be coated rapidly. Since paints are formulated withpreferred pigment volume concentrations, by increasing the pigmentvolume with a low cost polymer layer, the cost of the paint can besubstantially reduced without any significant degradation in paintoptical properties.

In addition to using a polymer layer as an outside layer in anyembodiments disclosed herein, it is possible to have an inner polymerlayer that would also be a low cost method for increasing the pigmentvolume for selected embodiments. FIG. 7 shows an embodiment of areflective coating 80 which has a base layer 82 formed as analuminum/polymer/aluminum layered structure with a polymer layer 84having top and bottom surfaces 86, 88. For this polymer layer 84, theoptical properties of the polymer are not critical since this polymerlayer is surrounded by opaque aluminum layer 90. The polymer layer 84 issimilar to the polymer layer 72, but has the top and bottom surfaces 86,88 respectively that are coated with the aluminum layer 90. Thedielectric layer 66 is formed on the aluminum layer 90, and the absorberlayer 68 is formed on the dielectric layer. The polymer layer can bedesigned to form a substantial portion of the base layer 82.

FIG. 8A illustrates another embodiment of a reflective pigment 100 thathas a layered stack similar to the reflective pigment 52 of FIG. 5B.Additionally, a second dielectric layer 102 is provided. The additionaldielectric layer 102 facilitates further color and solar near-infraredreflectance values. In this embodiment, thicknesses of the layers can befrom about 25 to 500 nm for the second dielectric layer 102, 10 to 100nm for the absorber layer 68, and 10 to 220 nm for the first dielectriclayer 66. The dielectric layers can be formed to have an index ofrefraction at 550 nm of about 1.3 to 2.5. The absorber layer 68preferably is formed of a semiconductor material such as amorphous Si,and generally has the properties of absorber layers previouslydisclosed. The dielectric layers are preferably formed of siliconnitride, and generally have the properties of the dielectric layerspreviously disclosed.

FIG. 8B illustrates another embodiment of a reflective pigment 103.Additionally, a second absorber layer 104 is provided. The additionalabsorber layer 104 facilitates further color and solar near-infraredreflectance values. In this embodiment, thicknesses of the layers can befrom about 1 to 200 nm for the second absorber layer 104, 90 to 200 nmfor the second dielectric layer 102, 10 to 100 nm for the first absorberlayer 68, and 10-220 nm for the first dielectric layer 66. Thedielectric layers 66, 102 can be formed to have an index of refractionat 550 nm of about 1.3 to 2.5. The absorber layers 68 and 104 preferablyare formed of a semiconductor material such as amorphous Si, andgenerally have the properties of absorber layers previously disclosed.

FIG. 9 shows another embodiment of a reflective pigment 105 that has anadditional dielectric layer 106 formed on the second absorber layer 104of the embodiment of FIG. 8A. The additional dielectric layer 106 can bea silicon nitride layer, and like the other dielectric layers preferablyhas an index of refraction at 550 nm of about 1.3 to 2.5. In thisembodiment, the first dielectric layer 66 preferably has a thickness ofabout 30 to 150 nm and the first absorber layer 68 has a thickness ofabout 40 to 80 nm. The second dielectric layer 102 has a thickness ofabout 90 to 200 nm, the second absorber layer 104 has a thickness ofabout 2 to 10 nm, and the third dielectric layer 106 has a thickness ofabout 30 to 500 nm. Similar to the other embodiments of the reflectivepigments, particular select combinations of the thicknesses of thelayers provides a wide gamut of cool color combinations with improvedspectral characteristics.

These improved spectral characteristics of the reflective coatings areexemplified in FIGS. 10 and 11 which illustrate percentage ofreflectance versus wavelength characteristics of two cool colorreflective coatings attached to a releasable substrate. FIG. 10 showsthe total reflectance vs. wavelength for a release coated Mylar filmwith an opaque evaporated aluminum layer having a thickness of about 200nm, a first silicon nitride layer having a thickness of 104 nm, a firstsilicon layer having a thickness of 56 nm, a second silicon nitridelayer having a thickness of 150 nm, a second silicon layer having athickness of 3.7 nm, and a third silicon nitride layer having athickness of 55 nm.

Similarly, FIG. 11 shows the total reflectance vs. wavelength for areflective coating on a release coated Mylar film with an opaqueevaporated aluminum having a thickness of 200 nm, a first siliconnitride layer having a thickness of 104 nm, a first silicon layer havinga thickness of 56 nm, and a second silicon nitride layer having athickness of 120 nm, a second silicon layer having a thickness of 3.7nm, and a third silicon nitride layer having a thickness of 50 nm. Ascan be seen in both FIGS. 10 and 11, the average reflectance in thesolar near-infrared region of 800 to 2500 nm is high. In particular, theaverage reflectance is greater than 75% in the solar near-infraredregion wavelength region. In the visible light region of 400 to 700 nm,the reflectance and hence average reflectance is much lower than theaverage reflectance in the solar near-infrared region. Due to thesereflective characteristics of the reflective pigments as designedherein, it is possible to have opaque dark visual colors that have highreflectance of solar near-infrared radiation compared to products usingconventional reflective multilayer pigments or conventional coolpigments.

Turning now to FIG. 12, a process for producing a reflective pigment isgenerally shown as 200. The present process 200 illustrates formation ofthe reflective pigment 52 shown in FIG. 5A. However, other steps whichadd one or more additional polymer, dielectric, and/or absorber layersare contemplated with the present process. Moreover, the particulararrangement of the layers can vary depending upon the desired stackingof the layers. For example, the polymer layer can be an inner layer oran outer layer. To facilitate understanding of the stacking process toform the reflective pigment, each absorber layer and dielectric layer ispartitioned into two layers that are deposited upon the stackedstructure in separate steps. However, with respect to the process offorming a reflective pigment is should be understood that the steps offorming a dielectric layer, such as dielectric layer 66 in FIG. 5A, aredefined as separate dielectric layer formation steps to facilitateunderstanding of the stacking process. However, a single step process offorming a dielectric or absorber layer as discussed herein with respectto the process would apply to forming an absorber or dielectric layer ina reflective coating process. In the case of the reflective coatingprocess, the coating would not be released from the substrate but wouldremain permanently attached to the substrate.

The process 200 starts at step 202 wherein a particular color and solarnear-infrared reflectance goal is selected for the cool color reflectivepigment to be fabricated. Based on this selection, the thicknesses ofthe layers are tailored to achieve the desired color and solarnear-infrared reflectance. The process then proceeds to step 204 whereina releasable substrate is provided. The releasable substrate preferablyis a Mylar film having a release layer thereon. Next, a first portion ofthe absorber layer is formed on the releasable substrate at step 206.The first portion absorber layer preferably is an amorphous siliconlayer. The process then proceeds to step 208 and provides a firstportion of a dielectric layer on the first portion absorber layer.Preferably, the first portion dielectric layer is a silicon nitridelayer.

A base layer is then formed on the first portion dielectric layer atstep 210. The base layer can be formed of a single metal layer orstacked structure which includes a polymer layer as discussed above.Preferably, the base layer is an aluminum layer. Step 212 has the secondportion of the dielectric layer formed on the base layer. Similarmaterials as the first portion dielectric layer can be used for thesecond portion dielectric layer. At step 214, a second portion of theabsorber layer is provided on the second portion dielectric layer, andcan be formed of similar materials as the first portion absorber layer.

Next, at step 216 the releasable substrate is removed from the firstportion absorber layer to produce the reflecting pigment. Optionally, achoice can be included at step 218 to determine whether or not thereflective pigment should be stored (NO) for further use in a binder orother mixture, or formed as a colored composition (YES). If no coloredcomposition is desired, then the process proceeds to step 220, storesthe reflective pigment, and then ends at step 222. Otherwise, if acolored composition is desired, then a polymer medium is provided atstep 224 and the reflective pigment is dispersed within the polymermedium at step 226. Next, the colored composition is stored at step 228and the process ends at step 222.

As discussed above, the substrate in each of these embodiments forreflective pigments is releasable, which allows the reflective pigmentto be separated from the substrate after the various layers have beenapplied to the substrate. Moreover, at least some of these embodimentsfor reflective pigments it is envisioned that at least some layers areformed on the releasable substrate, and no layers are formed after thestacked structure is released from the substrate. Generally, thesubstrate is designed to be as wide as needed, and preferably has awidth of one to seven feet. While polyvinyl alcohol (PVA) release coatedMylar film is contemplated as being used as the preferred release coatedsubstrate for the embodiments discussed above, other release coatingsbesides PVA materials can be used such as those that require non-aqueoussolvents and are well known in the art.

While certain presently preferred embodiments of the invention have beenherein described, it is to be appreciated that variations, changes andmodifications may be made therein without departing from the scope ofthe invention, as defined by the appended claims. For example,additional absorber and dielectric layers could be added to theembodiments herein, or the layer thicknesses could be greater or lessthan those shown.

1. A reflective coating comprising: a base layer having a reflectivesurface; a dielectric layer formed on said reflective surface; and anabsorber layer formed on said dielectric layer formed on said reflectivesurface of said base layer; wherein an average reflectance of saidreflective coating for wavelengths of electromagnetic radiation in therange of 800 to 2500 nm irradiated upon said reflective coating isgreater than about 60% and an average reflectance of said reflectivecoating for wavelengths of electromagnetic radiation in the range of 400to 700 nm irradiated upon said reflecting coating is less than saidaverage reflectance of said reflective coating from 800 to 2500 nm. 2.The reflective coating of claim 1, wherein said dielectric layer has anindex of refraction at 550 nm of about 1.3 to 2.5 and an extinctioncoefficient for electromagnetic radiation in the wavelength range of 400to 2500 nm of less than about 0.1.
 3. The reflective coating of claim 2,wherein said absorber layer comprises a semiconductor material with aband gap of about 1.7 eV.
 4. The reflective coating of claim 1, whereinsaid absorber layer comprises a semiconductor material having a band gapof about 1.7 eV.
 5. The reflective coating of claim 1, wherein saiddielectric layer formed on said reflective surface of said base layerhas a thickness of about 10 to 220 nm, and said absorber layer has athickness of about 10 to 100 nm.
 6. The reflective coating of claim 1,further comprising a second dielectric layer being formed on saidabsorber layer, said second dielectric layer having an index ofrefraction at 550 nm of about 1.3 to 2.5 and an extinction coefficientfrom 400 to 2500 nm of less than about 0.1.
 7. The reflective coating ofclaim 6, wherein said dielectric layer formed on said reflective surfaceof said base layer has a thickness of about 10 to 220 nm, said absorberlayer has a thickness of about 10 to 100 nm, and said second dielectriclayer has a thickness of about 25 to 500 nm.
 8. The reflective coatingof claim 6, further comprising a second absorber layer formed on saidsecond dielectric layer.
 9. The reflective coating of claim 8, whereinsaid dielectric layer formed on said reflective surface of said baselayer has a thickness of about 10 to 220 nm, said absorber layer has athickness of about 10 to 100 nm, said second dielectric layer has athickness of about 90 to 200 nm, and said second absorber layer has athickness of about 1 to 200 nm.
 10. The reflective coating of claim 8,further comprising a third dielectric layer being formed on said secondabsorber layer, said third dielectric layer having an index ofrefraction at 550 nm of about 1.3 to 2.5 and an extinction coefficientfrom 400 to 2500 nm of less than about 0.1.
 11. The reflective coatingof claim 10, wherein said dielectric layer formed on said reflectivesurface of said base layer has a thickness of about 30 to 150 nm, saidabsorber layer formed on said dielectric layer formed on said reflectivesurface of said base layer has a thickness of about 40 to 80 nm, saidsecond dielectric layer has a thickness of about 90 to 200 nm, saidsecond absorber layer has a thickness of about 2 to 10 nm, and saidthird dielectric layer has a thickness of about 30 to 500 nm.
 12. Thereflective coating of claim 1, wherein said base layer is a metal layer.13. The reflective coating of claim 11, wherein said metal layer is analuminum layer.
 14. The reflective coating of claim 1, wherein saidabsorber layer comprises a semiconductor.
 15. The reflective coating ofclaim 14, wherein said semiconductor is silicon.
 16. The reflectivecoating of claim 15, wherein a structure of said semiconductor isamorphous.
 17. The reflective coating of claim 1, wherein said absorberlayer comprises amorphous silicon and said dielectric layer comprisesone of silicon nitride, silicon dioxide, nitrides, oxides and fluorides.18. The reflective coating of claim 1, wherein said absorber layer hasan n/k value greater than about 10 at 700 nm and greater than about 100at 1250 nm, where n is the refractive index of the absorber layer and kis the extinction coefficient of the absorber layer.
 19. The reflectivecoating of claim 1, wherein said dielectric layer comprises siliconnitride.
 20. The reflective coating of claim 1, wherein the averagereflectance is greater than about 75% for wavelengths of electromagneticradiation in the range of 800 to 2500 nm.
 21. A reflective pigmentcomprising: a base layer having a top reflective surface and a bottomreflective surface; a dielectric layer formed on said top and bottomsurfaces of said base layer; and an absorber layer formed on saiddielectric layer formed on said top and bottom surfaces of said baselayer; wherein said dielectric layer has an index of refraction at 550nm of about 1.3 to 2.5, and wherein an average reflectance of saidpigment for wavelengths of electromagnetic radiation in the range of 800to 2500 nm irradiated upon said reflective pigment is greater than about60% and an average reflectance of said reflective coating forwavelengths of electromagnetic radiation in the range of 400 to 700 nmirradiated upon said reflecting coating is less than said averagereflectance of said reflective coating from 800 to 2500 nm.
 22. Thereflective pigment of claim 21, further comprising a polymer layer beingformed on said absorber layer.
 23. The reflective pigment of claim 21,further comprising a second dielectric layer being formed on saidabsorber layer, said second dielectric layer having an index ofrefraction at 550 nm of about 1.3 to 2.5.
 24. The reflective pigment ofclaim 23, further comprising a polymer layer being formed on said seconddielectric layer.
 25. The reflective pigment of claim 21, wherein saiddielectric layer formed on said top and bottom surfaces of said baselayer has a thickness of about 10 to 220 nm, and said absorber layer hasa thickness of about 10 to 100 nm.
 26. The reflective pigment of claim23, wherein said dielectric layer formed on said top and bottom surfacesof said base layer has a thickness of about 10 to 220 nm, said absorberlayer has a thickness of about 10 to 100 nm, and said second dielectriclayer has a thickness of about 25 to 500 nm.
 27. The reflective pigmentof claim 23, further comprising a second absorber layer formed on saidsecond dielectric layer.
 28. The reflective pigment of claim 27, furthercomprising a polymer layer formed on said second absorber layer.
 29. Thereflective pigment of claim 27, wherein said dielectric layer formed onsaid top and bottom surfaces of said base layer has a thickness of about10 to 220 nm, said absorber layer formed on said dielectric layer formedon said top and bottom surfaces of said base layer has a thickness ofabout 10 to 100 nm, said second dielectric layer has a thickness ofabout 90 to 200 nm, and said second absorber layer has a thickness ofabout 1 to 200 nm.
 30. The reflective pigment of claim 27, furthercomprising a third dielectric layer being formed on said second absorberlayer, said third dielectric layer having an index of refraction at 550nm of about 1.3 to 2.5.
 31. The reflective pigment of claim 30, furthercomprising a polymer layer being formed on said third dielectric layer.32. The reflective pigment of claim 30, wherein said dielectric layerformed on said top and bottom surfaces of said base layer has athickness of about 30 to 150 nm, said absorber layer formed on saiddielectric layer formed on said top and bottom surfaces of said baselayer has a thickness of about 40 to 80 nm, said second dielectric layerhas a thickness of about 90 to 200 nm, said second absorber layer has athickness of about 2 to 10 nm, and said third dielectric layer has athickness of about 30 to 500 nm.
 33. The reflective pigment of claim 21,wherein said base layer is an aluminum/polymer/aluminum layeredstructure.
 34. The reflective pigment of claim 33, wherein said polymerlayer has a thickness of about 1000 to 3000 nm.
 35. The reflectivepigment of claim 21, wherein said absorber layer is a semiconductorlayer having a band gap of about 1.7 eV.
 36. The reflective pigment ofclaim 21 wherein said absorber layer comprises silicon.
 37. A process ofproducing a reflecting pigment comprising the steps of: providing areleasable substrate; providing a first absorber layer on saidreleasable substrate; providing a first dielectric layer on said firstabsorber layer; providing a base layer on said first dielectric layer;providing a second dielectric layer on said base layer; providing asecond absorber layer on said second dielectric layer; and removing saidreleasable substrate from said first absorber layer to produce saidreflecting pigment.
 38. The process of claim 37, wherein said releasablesubstrate is a plastic film having a release layer deposited thereon.39. The process of claim 37, wherein said first and second dielectriclayers have indices of refraction of about 1.3 to 2.5.
 40. The processof claim 37, wherein said reflecting pigment has an average reflectancegreater than or equal to 60% for wavelengths of electromagneticradiation in the range of 800 to 2500 nm irradiated upon said reflectingpigment and an average reflectance of said reflective pigment forwavelengths of electromagnetic radiation in the range of 400 to 700 nmirradiated upon said reflecting pigment is less than said averagereflectance of said reflective pigment from 800 to 2500 nm.
 41. Theprocess of claim 37, wherein said base layer is an aluminum layer. 42.The process of claim 37, wherein said base layer is analuminum/polymer/aluminum layered structure.
 43. The process of claim37, further comprising a step of forming a polymer layer on saidreleasable substrate, said first absorber layer being directly formed onsaid polymer layer.
 44. The process of claim 43, further comprising astep of forming a second polymer layer on said second dielectric layerprior to removing said reflecting pigment from said releasablesubstrate.
 45. The process of claim 37, further comprising the steps of:providing a third dielectric layer directly on said releasablesubstrate, said first absorber layer being directly formed on said thirddielectric layer; and providing a fourth dielectric layer on said secondabsorber layer.
 46. The process of claim 37, further comprising thesteps of: providing a third dielectric layer on said releasablesubstrate, said first absorber layer being formed on said thirddielectric layer; providing a fourth dielectric layer on said secondabsorber layer; providing a third absorber layer directly on saidreleasable substrate, said third dielectric layer being directly formedon said third absorber layer; and providing a fourth absorber layer onsaid fourth dielectric layer.
 47. The process of claim 37, furthercomprising the steps of: providing a third dielectric layer on saidreleasable substrate, said first absorber layer being formed on saidthird dielectric layer; providing a fourth dielectric layer on saidsecond absorber layer; providing a third absorber layer on saidreleasable substrate, said third dielectric layer being formed on saidthird absorber layer; providing a fourth absorber layer on said fourthdielectric layer; providing a fifth dielectric layer directly on saidreleasable substrate, said third absorber layer being directly formed onsaid fifth dielectric layer; and providing a sixth dielectric layer onsaid fourth absorber layer.
 48. The process of claim 37, wherein saidabsorber layer is sputter deposited amorphous silicon.
 49. A coloredcomposition, comprising: a polymer medium; and a plurality of reflectivepigments dispersed in said polymer medium, each reflective pigmentcomprising: a base layer having a top reflective surface and a bottomreflective surface; a dielectric layer formed on said top and bottomsurfaces of said base layer; and an absorber layer formed on saiddielectric layer formed on said top and bottom surfaces of said baselayer, wherein said dielectric layer has an index of refraction at 550nm of about 1.3 to 2.5 and an average reflectance of said reflectivepigment for wavelengths of electromagnetic radiation in the range of 800to 2500 nm irradiated upon said reflecting pigment is greater than about60% and an average reflectance of said reflective pigment forwavelengths of electromagnetic radiation in the range of 400 to 700 nmirradiated upon said reflecting pigment is less than said averagereflectance of said reflective pigment from 800 to 2500 nm.
 50. Thecomposition of claim 49, wherein the polymer medium is a paint or ink.